The present invention relates to vegetables and herbs and particularly to a method for the preservation of such foodstuffs.
Vegetables and herbs are widely used in processed-foods because of their taste and flavor properties. Besides the flavoring properties, vegetables and herbs are useful to impart a nice and pleasant colored aspect to food products. Herbs are used in the composition of numerous traditional dishes and the aroma and color of various specific herbs are of great importance in these.
Thus, basil, olives, tomato, bell pepper, garlic, onion, carrot, coriander or mint, for example, do not only impart a pleasant typical flavor but also an attractive color. Since herbs are seasonal and particularly sensitive to spoilage because of their high water content they are mainly found in dried form. However, most herbs and vegetables when dried, lose their green color. Aroma and flavor are also irreversibly altered so that they do not represent satisfactory alternative to freshly picked herbs.
“Freshness” is a universal quality issue with processed foods and this is of particular interest for herbs and vegetables because such products inherently refer to freshness. Regarding herbs, the green color aspect is considered as a key factor for assessment of this freshness and because of all the processes that herbs may be subjected to, the green color is quite often adversely affected.
The chemical basis for the loss of bright green color of fresh vegetables and herbs has been extensively studied. Thus, chlorophyll, which is responsible for this bright green color degrades during thermal processing such as drying, for example. However, in non heat-treated food products, the green color is also dictated by the chemical stability of the chlorophyll which has been shown to be acid sensitive and to have its maximal stability and therefore its maximal green color aspect at pH of about 7 and slightly above.
In the particular case of culinary applications, herbs and/or vegetables are intimately mixed or ground. Mixing or grounding even accelerate spoilage. The product can therefore not be stored for a long time without any preservatives.
Microbial stabilization may be achieved by lowering the pH by addition of acids and/or lowering the water activity (Aw) thanks to addition of salts as well as addition of anti-microbial additives like sulfites or sorbate.
Dehydrated products have a typical Aw of about 0.2 to 0.3 and are therefore microbiologically stable since no organisms can grow at Aw below about 0.6 to 0.65. At Aw higher than about 0.6 to 0.65, microbial growth can occur causing spoilage, formation of off-odors as well as infection with pathogenic microorganisms and/or toxins. Since the perception of freshness in ambient stable products may be obtained at Aw of about 0.6 to 0.65, the prevention of microbial growth may be achieved by addition of preservatives and/or reduction of pH. But, as said before, chlorophyll is not stable anymore and therefore the green color disappears at acidic pH.
Some attempts have been made to obtain shelf stable vegetables or herbs with improved color. U.S. Pat. No. 5,858,446 relates to fresh herbs with bright and fresh color that can be used for culinary applications and that can be stored for protracted periods. It is taught that the leaves of aromatic plants are mixed in the absence of oxygen with either a salt and/or an oxygen scavenging agent in order to obtain a water activity of the mixture below 0.9.
European patent no. 87,717 discloses a dried vegetable product manufacturing process in which a plant is stabilized by heating and addition of electrolyte before drying with a carrier.
U.S. Pat. No. 4,832,969 discloses dried green vegetables with superior color retention. The manufacture of such dried vegetables comprises the steps of blanching the pieces of vegetables in a bath having a pH of about 7 to 9, infusing the blanched vegetable pieces in a solution comprising sugar alcohol, sugar and bittering agents such KCl or MgCl2 and finally drying the vegetable pieces to an Aw of 0.3 to 0.85.
All these prior art technologies are complicated and involve the use of various chemical preservatives that are not always well perceived by the consumer. Moreover, these prior technologies refers to dried products that do not bring the freshness to the consumer. Therefore, there remains a need for shelf stable herbs or vegetables compositions that exhibit a bright and attractive green color.